T cell co-stimulatory and co-inhibitory molecules (collectively named co-signaling molecules) play a crucial role in regulating T cell activation, subset differentiation, effector function and survival (Chen et al 2013, Nature Rev. Immunol. 13: 227-242). Following recognition of cognate peptide-MHC complexes on antigen-presenting cells by the T cell receptor, co-signaling receptors co-localize with T cell receptors at the immune synapse, where they synergize with TCR signaling to promote or inhibit T cell activation and function (Flies et al 2011, Yale J. Biol. Med. 84: 409-421). The ultimate immune response is regulated by a balance between co-stimulatory and co-inhibitory signals (“immune checkpoints”) (Pardoll 2012, Nature Reviews Cancer 12: 252-264). Lymphocyte activation gene-3 (LAG3) functions as one such ‘immune checkpoint’ in mediating peripheral T cell tolerance.
LAG3 (also called CD223) is a 503 amino acid transmembrane protein receptor expressed on activated CD4 and CD8 T cells, γδ T cells, natural killer T cells, B-cells, natural killer cells, plasmacytoid dendritic cells and regulatory T cells. LAG3 is a member of the immunoglobulin (Ig) superfamily. The primary function of LAG3 is to attenuate the immune response. LAG3 binding to MHC class II molecules results in delivery of a negative signal to LAG3-expressing cells and down-regulates antigen-dependent CD4 and CD8 T cell responses. LAG3 negatively regulates the ability of T cells to proliferate, produce cytokines and lyse target cells, termed as ‘exhaustion’ of T cells. LAG3 is also reported to play a role in enhancing T regulatory (Treg) cell function (Pardoll 2012, Nature Reviews Cancer 12: 252-264).
Since LAG3 plays an important role in tumor immunity and infectious immunity, it is an ideal target for immunotherapy. Blocking LAG3 with antagonists, including monoclonal antibodies, has been studied in treatments of cancer and chronic viral infections (Turnis et al 2015, Eur. J. Immunol. 45: 1892-1905).
Monoclonal antibodies to LAG3 are known in the art and have been described, for example, in U.S. Pat. Nos. 5,976,877, 6,143,273, 6,197,524, 8,551,481, 20110070238, 20110150892, 20130095114, 20140093511, 20140127226, 20140286935, and in WO95/30750, WO97/03695, WO98/58059, WO2004/078928, WO2008/132601, WO2010/019570, WO2014/008218, EP0510079B1, EP0758383B1, EP0843557B1, EP0977856B1, EP1897548B2, EP2142210A1, and EP2320940B1.
When developing an immunotherapy for treating human beings, there is a need for antibodies exhibiting properties such as low immunogenicity, suitable binding kinetics parameters, cross-reactivity to the monkey target, suitable in vitro activity and/or suitable in vivo activity.